How do i change my network key to wep not wpa?

Ok so i have a nintendo ds . . And it wont connect using WIFI so i went on the internet and Read that i half to change my wpa to wep?? if soo how do i do that???How do i change my network key to wep not wpa?
if u have a modem with router or router it self login to the website edit settings or something find wep, wpa, etc. and change itHow do i change my network key to wep not wpa?
what is the name of your router??

go to a computer connected to your wireless...thingy

and go 192.168.0.1 in the address bar of an internet window,

tell me what pops up
Go into your routers GUI and click on the Wireless Tab and then Security the settings are there. Remember to write down your encryption code.